# Molecular mechanism of Norrin signaling through Frizzled4 and LRP5/6

> **NIH NIH F31** · STANFORD UNIVERSITY · 2022 · $40,615

## Abstract

Rationale: Aberrant retinal neovascularization and compromised blood-retina barrier (BRB) integrity causes
vision loss in various diseases. Signaling by the secreted ligand Norrin directs development and maintenance of
the BRB through activation of the Wnt/b-catenin pathway. In this pathway, Norrin acts through receptors Frizzled-
4 (Fzd4) and Low-density lipoprotein receptor-related protein 5 or 6 (LRP5/6), leading to the intracellular
membrane recruitment of the transducer Dishevelled (Dvl) and ultimately, the stabilization of transcriptional
coactivator b-catenin for transcription of target genes. While this pathway has been studied in cellular and
developmental models, a biochemical understanding of pathway activation, and specifically how receptors
transmit the Norrin-binding signal across the membrane to recruit Dvl, constitutes a gap in knowledge.
Objective: Using purified proteins, the proposed work will rigorously characterize molecular interactions within
the ligand/receptor/coreceptor/transducer complex and determine the physical basis for Norrin-induced
transducer recruitment. An allosteric model in which conformational changes within the Norrin/Fzd/LRP complex
cause Fzd to recruit Dvl with high affinity will be tested.
Approach: Aim 1 quantifies allosteric coupling between components of the Norrin/Fzd/LRP/Dvl complex.
Binding assays will be conducted in a membrane environment to determine the extent to which Norrin and LRP
influence Fzd recruitment of Dvl. Aim 2 identifies to structural basis of signaling in the Norrin/Fzd/LRP/Dvl
complex. Cryo-electron microscopy (cryo-EM) structures of the Norrin/Fzd/LRP complex will be pursued with
and without bound Dvl DEP domain. The functional relevance of structurally important residues will be tested in
cell-based transcriptional reporter assays.
Outcomes: These biochemical and structural studies will uncover the physical basis of the initiating events in
Norrin/β-catenin signaling. Mechanistic insight will 1) provide a valuable framework from which to understand
receptor activation, 2) reveal the physical basis of genetic defects affecting this pathway, and 3) inform strategies
to specifically and rationally target this pathway in the retina. Additionally, these results will be translatable to the
broader Wnt/b-catenin signaling pathway, contributing to studies of this developmental pathway as a target in
regenerative medicine and oncology.

## Key facts

- **NIH application ID:** 10456949
- **Project number:** 5F31EY031947-03
- **Recipient organization:** STANFORD UNIVERSITY
- **Principal Investigator:** Elise Bruguera
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $40,615
- **Award type:** 5
- **Project period:** 2020-08-04 → 2023-08-03

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10456949

## Citation

> US National Institutes of Health, RePORTER application 10456949, Molecular mechanism of Norrin signaling through Frizzled4 and LRP5/6 (5F31EY031947-03). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10456949. Licensed CC0.

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